This invention relates to the production of alkylated aromatic compounds such as, for example, alkyl naphthalenes and substituted alkyl naphthalenes.
Alkylaromatic fluids have been proposed for use as certain types of functional fluids in which good thermal and oxidative properties are required. For example, U.S. Pat. No. 4,714,794 describes the monoalkylated naphthalenes as having excellent thermal and oxidative stability, low vapor pressure and flash point, good fluidity and high heat transfer capacity and other properties which render them suitable for use as thermal medium oils. The use of a mixture of monoalkylated and polyalkylated naphthalenes as a base for synthetic functional fluids is described in U.S. Pat. No. 4,604,491. U.S. Pat. Nos. 4,211,665 and 4,238,343 describe the use of alkylaromatics as transformer oils.
Alkylated naphthalenes are usually produced by the alkylation of naphthalene or a substituted naphthalene in the presence of an acidic alkylation catalyst such as a Friedel-Crafts catalyst, for example, an acidic clay as described in U.S. Pat. Nos. 4,714,794 or 4,604,491, or a Lewis acid such as aluminum trichloride as described in U.S. Pat. Nos. 4,211,665 and 4,238,343. The use of a collapsed silica-alumina zeolite for the catalytic alkylation of aromatic compounds such as naphthalene is disclosed in U.S. Pat. No. 4,570,027. The use of various zeolites including intermediate pore size zeolites such as ZSM-5 and large pore size zeolites such as zeolite L and ZSM-4 for the alkylation of various monocyclic aromatics such as benzene is disclosed in U.S. Pat. No. 4,301,316.
In the formulation of functional fluids based on the alkyl naphthalenes, it has been found that the preferred alkyl naphthalenes include the mono-substituted naphthalenes since they provide the best combination of properties in the finished product. Because the mono-alkylated naphthalenes posses fewer benzylic hydrogens than the corresponding di-substituted or polysubstituted versions, they have better oxidative stability and therefore form better functional fluids and additives. In addition, the mono-substituted naphthalenes have a kinematic viscosity in the desirable range of about 5-8 cSt (at 100xc2x0 C.) when having alkyl substituents of about 14 to about 18 carbon atoms chain length. Although the mono-alkylated naphthalenes may be obtained in admixture with more highly alkylated naphthalenes using conventional Friedel-Crafts catalysts such as those mentioned above, or by the use of zeolites such as USY, the selectivity to the desired mono-alkylated naphthalenes is not as high as desired.
Several recent advances have been made in this area which improve the yields of the desired mono-alkylated naphthenes.
U.S. Pat. No. 5,034,563 to Ashjian et al., which is incorporated herein by reference in its entirety, teaches use of a zeolite containing a bulky cation. The use of, e.g., USY with cations having a radius of at least about 2.5 Angstroms increases selectivity for desired products. Taught as suitable were zeolites containing hydrated cations of metals of Group IA, divalent cations, especially of Group IIA, and cations of the Rare Earths. The patent had examples in which H+, NH4+, and Na+ were added to USY zeolite by a procedure involving forming a slurry of zeolite and liquid, 1 hour of stirring, decantation, and a repeat of the exchange procedure.
U.S. Pat. No. 5,177,284, which is incorporated herein by reference in its entirety, discusses the desirable properties of alkylated naphthalene fluids with higher alpha:beta ratios, including improved thermal and oxidative stability. Le et al. found that several parameters influenced the alpha:beta ratio of the alkylated naphthalene products, including steaming the zeolite, lowering the alkylation temperature, or the use of acid-treated clay. Steamed USY catalyst gave excellent results in the examples. The patent also discloses use of zeolites with reduced activity due to base exchange, alkaline earth ion exchange, and use of boron-zeolite beta.
U.S. Pat. No. 5,191,135, which is incorporated herein by reference in its entirety, discloses the effect of co-feeding water for this reaction when using a large pore zeolite catalyst, such as zeolite Y. Adding from 1-3 wt % water to the feed improved the alkylation reaction, a result attributed to suppression of zeolite acid site activity.
U.S. Pat. No. 5,191,134, which is incorporated herein by reference in its entirety, disclosed a similar alkylation process using MCM-41.
U.S. Pat. No. 5,457,254 to Ardito et al., which is incorporated herein by reference in its entirety, discloses a naphthalene alkylation process whereby the presence of both ammonium and protonic species increases selectivity for production of long chain mono-alkyl substituted naphthalenes.
The present inventors did additional work to further improve this alkylation process, and to increase the efficiency of the reaction both in terms of conversion and yield.
The present inventors have discovered that an alkylation catalyst comprising a large pore zeolite which has been dealuminated to remove non-framework aluminum by selective ion exchange in acidic conditions, provides unexpectedly superior activity over a corresponding catalyst without the dealumination treatment. The inventors also discovered that the catalyst of the invention is effective in alkylation of other compounds containing two aromatic rings including, but not limited to, diphenyl oxide, diphenyl sulfide, diphenyl methane, and biphenyl.
Accordingly, the present invention provides a process for preparing alkyl substituted aromatic compounds, including long chain alkyl substituted aromatic compounds, which comprises alkylating an aromatic compound with an alkylating agent possessing an alkylating aliphatic group having at least six carbon atoms under alkylation reaction conditions in the presence of an alkylation catalyst comprising a porous, crystalline zeolite which has been selectively dealuminated, under acidic conditions, to remove non-framework aluminum. Additionally, the present invention provides a catalyst comprising a USY zeolite having a unit cell size from about 2.440 to about 2.464 nm and a bulk silica:alumina ratio of about 6.5 to about 10.0, wherein the non-framework aluminum content ranges from about 0 to about 25% of the total aluminum content.
The starting materials for the production of the alkylated aromatic compounds include the aromatic compounds themselves. The term xe2x80x9caromatic compoundxe2x80x9d is understood by those of ordinary skill in the art to refer to any compound having at least one aromatic ring, including, but not limited to, benzene, pyridine, naphthalene. The aromatic compound may be unsubstituted or substituted with, by way of non-limiting examples, halogen, alkyl, alkenyl, nitro, amino, amido, carboxyl, carboxamido, etc. Naphthalenes include naphthalene itself as well the substituted naphthalenes which may contain, for example, one or more short chain alkyl groups containing up to about eight carbon atoms, such as methyl, ethyl or propyl. Suitable alkyl-substituted naphthalenes include, for example, alpha-methylnaphthalene, dimethylnaphthalene and ethylnaphthalene. Naphthalene itself is preferred since the resulting mono-alkylated products have better thermal and oxidative stability than the more highly alkylated materials for the reasons set forth above.
Various other aromatic chemical compounds containing one or two aromatic rings in the structure can also be alkylated by this process. Such compounds include, but are not limited to, alkylbenzenes such as benzene, toluene, xylenes, ethyl benzene, methylethyl benzene, trimethyl benzene, and propyl benzene. Also included are other two-ring aromatic compounds such as, for example, diphenyl oxide, diphenyl sulfide, diphenyl methane, biphenyl, and alkyl-substituted derivative compounds.
The alkylating agents which are used to alkylate the naphthalene include, but are not limited to, any aliphatic or aromatic organic compound having one or more available alkylating aliphatic groups capable of alkylating the naphthalene. The alkylating group itself should have at least about 6 carbon atoms, preferably at least about 8, and still more preferably at least about 12 carbon atoms. For the production of functional fluids and additives, the alkyl groups on the alkyl-naphthalene preferably have from about 12 to about 30 carbon atoms, with particular preference to about 14 to about 18 carbon atoms. A preferred class of alkylating agents is olefins with the requisite number of carbon atoms, including, but not limited to, the hexenes, heptenes, octenes, nonenes, decenes, undecenes, dodecenes, tridecenes, tetradecenes, pentadecenes, hexadecenes, heptadecenes, and octadecenes. Mixtures of the olefins, e.g., mixtures of C12 -C20 or C14-C18 olefins, are also useful. Branched alkylating agents, especially oligomerized olefins such as, for example, the trimers, tetramers, pentamers, etc., of light olefins including, but not limited to, ethylene, propylene, the butylenes, etc., are also useful. Other useful alkylating agents that may be used include alcohols (inclusive of monoalcohols, dialcohols, trialcohols, etc.) such as, for example, hexanols, heptanols, octanols, nonanols, decanols, undecanols, and dodecanols; and alkyl halides such as hexyl chlorides, octyl chlorides, dodecyl chlorides; and higher homologs.
The alkylation reaction between the naphthalene and the alkylating agent is carried out in the presence of a zeolite catalyst that contains a cation of certain specified radius. The molecular size of the alkylation products will require a relatively large pore size in the zeolite in order for the products to leave the zeolite, indicating the need for a relatively large pore size in the zeolite, which will also tend to reduce diffusion limitations with the long chain alkylating agents. The large pore size zeolites are the most useful zeolite catalysts for this purpose, although the less highly constrained intermediate pore size zeolites may also be used, as discussed below. The large pore size zeolites include, but are not limited to, zeolites such as faujasite, the synthetic faujasites (zeolites X and Y), zeolite L, ZSM-4, ZSM-18, ZSM-20, MCM-68, mordenite, and offretite, which are generally useful for this purpose, are characterized by the presence of a 12-membered oxygen ring system in the molecular structure and by the existence of pores with a minimum dimension of at least 7.4 {acute over (xc3x85)}, as described by Frilette et al. in J. Catalysis 67, 218-222 (1981). See also Chen et al., xe2x80x9cShape-Selective Catalysis in Industrial Applications,xe2x80x9d (Chemical Industries, Vol. 36) Marcel Dekker Inc., New York 1989, ISBN 0-8247-7856-1; and Hoelderich et al., Agnew. Chem. Int. Ed. Engl. 27, 226-246 (1988), especially pp.226-229. The large pore size zeolites may also be characterized by a xe2x80x9cConstraint Indexxe2x80x9d of not more than about 2, in most cases not more than about 1. Zeolite beta, a zeolite having a structure characterized by twelve-membered pore openings, is included in this class of zeolites although under certain circumstances it has a Constraint Index approaching the upper limit of about 2 which is characteristic of this class of zeolites. The method for determining Constraint Index is described in U.S. Pat. No. 4,016,218, together with values for typical zeolites and of the significance of the Index in U.S. Pat. No. 4,861,932, to which reference is made for a description of the test procedure and its interpretation.
Zeolites whose structure is that of a ten-membered oxygen ring, generally regarded as the intermediate pore size zeolites, may also be effective catalysts for this alkylation reaction if their structure is not too highly constrained. Thus, zeolites such as ZSM-12 (Constraint Index 2) may also be effective catalysts for this reaction. The zeolite identified as MCM-22 is a useful catalyst for this reaction. MCM-22 is described in U.S. patent application Ser. No. 07/254524, filed Oct. 6, 1988, and also in International Patent Application PCT/US88/04251, to which reference is made for a description of this zeolite. Thus, zeolites having a Cl up to about 3 will generally be useful catalysts, although the activity may be found to be dependent on the choice of alkylating agent, especially its chain length, a factor that imposes diffusion limitations upon the choice of zeolite. MCM-49 and MCM-56 are also useful catalysts according to the present invention.
A highly useful zeolite for the production of the monoalkylated naphthalenes is ultrastable Y, usually referred to as USY. When this material contains hydrated cations, it catalyses the alkylation in good yields with excellent selectivity. Zeolite USY is a material of commerce, available in large quantities as a catalyst for the cracking of petroleum. It is produced by the stabilization of zeolite Y by a procedure of repeated ammonium exchange and controlled steaming. Processes for the production of zeolite USY are described in U.S. Pat. Nos. 3,402,966, 3,923,192, and 3,449,070; see also Wojciechowski, xe2x80x9cCatalytic Cracking, Catalysts, Chemistry and Kinetics,xe2x80x9d (Chemical Industries, Vol. 25), Marcel Dekker, New York, 1986, ISBN 0-8247-7503-8, to which reference is made for a description of zeolite USY, its preparation and properties.
It is preferred to use a small crystal Y zeolite, ranging from about 0.2 to about 0.4 micron, although materials ranging from about 0.6 to about 1.3 micron, which is more typical of Y zeolite crystals, may also be used.
The alkylation reaction conditions include a temperature ranging from about 100xc2x0 C. to about 400xc2x0 C. and a pressure of from about 0.2 to about 25 atmospheres and a weight hourly space velocity of from about 0.1 to about 10. The mole ratio of the alkylatable aromatic to alkylating agent ranges from about 0.1:1 to about 50:1.
According to one aspect of the invention, an aromatic compound alkylation catalyst is provided which comprises a USY zeolite having a unit cell size from about 2.440 to about 2.464 nm, a bulk silica:alumina ratio of about 6.5 to about 10.0 and a non-framework aluminum content below about 25 percent of the bulk aluminum.
According to another aspect of the invention, an aromatic compound alkylation catalyst is provided which comprises a USY zeolite having a unit cell size from about 2.446 to about 2.460 nm, a bulk silica:alumina ratio of about 6.5 to about 9.0 and a non-framework aluminum content below about 25 percent of the bulk aluminum. In such a catalyst composition the molar ratio of nitrogen to protonic species is within the range of about 80:20 to about 20:80.